Historically, phosphates have been used as builders for detergents, including automatic dishwashing (ADW) detergents, due to their excellent chelating agent performance. However, due to aquatic plant stimulation effects, most jurisdictions have limited or banned the use of phosphates in detergents. In the absence of chelating phosphates, there has been an important need for development of new and effective chelating agents, dispersants, and/or builders for ADW detergents having little or no phosphate in them. Polyacrylate dispersants are known to inhibit crystal growth and assist with particle dispersion. Amino carboxylates stoichiometrically bind metal ions, thereby enhancing scale inhibition, and are being explored as another class of chelants that may replace phosphates in detergents and other aqueous systems.
(Meth)acrylic acid based polymers have been found to provide good anti-redeposition characteristics in laundry detergents, as described in International Patent Application Publication No. WO 2007/089001. The polymers described in WO 2007/089001 were derived from (meth)acrylic acid monomers, (meth)acrylate monomers, and one or more other monomers such as those having amino, hydroxyl or sulfonic functional groups. These polymers had weight average molecular weight (MWw) from 2,000 to 100,000, most preferably from 4,000 to 60,000 and, according to WO 2007/089001, a MWw. “less than 2,000 reduces dispersibility for soil and could reduce also prevention capability of soil redeposition,” which clearly advises against use of such polymer having MWw less than about 2,000.
United States Patent Application Publication No. US 2008/0262192 disclosed water soluble polymers derived from amino group-containing allyl monomers and useful as cleaners, water-treatment agents and fiber treatment agents. These polymers are characterized as having a molecular weight distribution of 12 or less, and MWw from 1,000 to 100,000, most preferably from 5,000 to 20,000.
A family of patents which includes U.S. Pat. Nos. 4,906,383 and 4,913,880 described polymers useful for water treatment and derived from α-, β-ethylenically unsaturated monomers, which contain carboxylic acid or carboxylic amide functionalities, and amine-containing allyl ether monomers. These patents taught that the amine-containing allyl ether monomers were derived from the ring opening reaction of a (meth)allylic glycidyl ether, preferably allyl glycidyl ether (AGE), with ammonia, primary, secondary or tertiary amines, for example carboxylate-containing amines such as iminodiacetic acid (IDA). It was contemplated that these polymers, comprising both amine and carboxylic functionalities, would be useful in a broad range of water treatment applications including scale inhibition in water systems such as cooling, boiler, gas scrubbing, and pulp and paper manufacturing systems, as well as corrosion inhibitors and chelating activity for various metal ions in solution. It was further stated that such polymers may be used to prevent precipitation of various calcium-based fouling solids, as well as various metal oxide and metal hydroxide deposits, in water systems.
Moreover, polyacrylate polymers which contain sulfonic acid monomers, such as 2-acrylamido-2-methylpropane sulfonic acid (AMPS), are known to provide good inhibition against silica-based scale formation. Polymers commercially available under the tradename ACUSOL 588 from Dow Chemical Company contain acrylic acid and AMPS monomers and have been marketed for use in ADW detergents to control silica- and phosphorus-based scales. With the advent of phosphorus-free ADW detergents, ACUSOL 588 and similar dispersants remain effective at controlling silica-based scale.
Chelants may be added to phosphorus-free ADW detergents to aid scale inhibition. For example, methylglycine diacetic acid (MGDA) is commonly used in ADW detergents in place of phosphorus to bind calcium and magnesium ions and thereby inhibit formation of carbonate-based scales. However, MGDA is known to cause equipment corrosion in high amounts and lead to formation of nitriloacetic acid (NTA), a known carcinogen. Thus, if other chelants can be identified as effective for inhibiting scale formation in phosphate-free ADW detergents, all or a portion of the MGDA could be replaced by such other chelants without reduction of detergent effectiveness.
Notwithstanding the foregoing developments, there remains a need for anti-scaling agents for ADW detergents to replace the now-disfavored phosphates that previously inhibited scale build-up.